Parabolic reflectors can be constructed by shaping a flexible material to the parabolic shape. This is accomplished by bending the flexible material to form a parabola. In some instances, the parabola may be formed by molding the material to the parabolic shape and coating it with a suitable material.
In U.S. Pat. No. 4,115,177, a tool is provided for manufacturing parabolic solar reflectors. The tool employs an improved smooth convex parabolic surface terminating in edges remote from the parabolic vertex which are preferably placed under elastic tension tending to draw the edges toward each other. The improved convex surface is a film of plastic coated with chromium metal on its exterior surface. A multiple layered thermosetting plastic reflector support is molded onto the convex surface of the tool. The reflector support is removed from the tool and a layer of aluminum is vacuum deposited onto the interior concave parabolic reflector surface.
In U.S. Pat. No. 4,571,812, a solar concentrator of substantially parabolic shape is formed by preforming a sheet of highly reflective material into an arcuate section having opposed longitudinal edges and having a predetermined radius of curvature and applying a force to at least one of the opposed edges of the section to move the edges toward each other and into a predetermined substantially parabolic configuration and then supporting it.
A parabolic trough solar collector using reflective flexible materials is disclosed in U.S. Pat. No. 4,493,313. A parabolic cylinder mirror is formed by stretching a flexible reflecting material between two parabolic end formers. The formers are held in place by a spreader bar. The resulting mirror is made to track the sun, focusing the sun's rays on a receiver tube. The ends of the reflective material are attached by glue or other suitable means to attachment straps. The flexible mirror is then attached to the formers. The attachment straps are mounted in brackets and tensioned by tightening associated nuts on the ends of the attachment straps. This serves both to stretch the flexible material orthogonal to the receiver tube and to hold the flexible material on the formers. The flexible mirror is stretched in the direction of the receiver tube by adjusting tensioning nuts. If materials with matching coefficients of expansion for temperature and humidity have been chosen, for example, aluminum foil for the flexible mirror and aluminum for the spreader bar, the mirror will stay in adjustment through temperature and humidity excursions. With dissimilar materials, e.g., aluminized mylar or other polymeric material and steel, spacers can be replaced with springs to maintain proper adjustment. The spreader bar cross section is chosen to be in the optic shadow of the receiver tube when tracking and not to intercept rays of the sun that would otherwise reach the receiver tube. This invention can also be used to make non-parabolic mirrors for other apparatus and applications.
In U.S. Pat. No. 4,348,798, an extended width parabolic trough solar collector is supported from pylons. A collector is formed from a center module and two wing modules are joined together along abutting edges by connecting means. A stressed skin monocoque construction is used for each of the modules.
In U.S. Pat. No. 4,135,493, a parabolic trough solar energy collector including an elongated support with a plurality of ribs secured thereto and extending outwardly therefrom. One surface of said ribs is shaped to define a parabola and is adapted to receive and support a thin reflecting sheet which forms a parabolic trough reflecting surface. One or more of said collectors are adapted to be joined end to end and supported for joint rotation to track the sun. A common drive system rotates the reflectors to track the sun; the reflector concentrates and focuses the energy along a focal line. The fluid to be heated is presented along the focal line in a suitable pipe which extends therealong.